After some playing around I found that the following format also works for Itunes movies, albeit it opens the Itunes Movie App rather than the Apple TV app. Not a big issue for me.
https://itunes.apple.com/us/movie/about-a-boy/id280781993?uo=4
Apple provides a web service, which if queried with a movie name returns a JSON file that includes the above URL. i.e.
https://itunes.apple.com/search?term="About a Boy"&entity=movie&releaseYearTerm=2003&limit=1
I'm not a programmer, but I'm OK with spreadsheets so I was able to create a Google Sheet which, using a custom JSON Import script I found online, was able to call the web service for a movie within my collection and return the iTunes URL. I then had a column within the Google Sheets which populated the echo script to add the .strmlnk file. In all, it took me around 30 minutes to import my 500 iTunes movies into Channels.
It's probably quite crude, but it worked for me as a one-off exercise. I've provided my GSheet below, which you can take a copy of, if you want to try it out - there are some caveats which are listed below.
Resources:
Apple Documentation on web service
https://affiliate.itunes.apple.com/resources/documentation/itunes-store-web-service-search-api/
Custom ImportJSON.gs
https://github.com/bradjasper/ImportJSON
First, export your iTunes collection by navigating to Films in Itunes, switching view to grid and selecting the Name and Release Year column. Paste into GSheet.
Column E URL from JSON will populate with Itunes Links
If #Error is shown, I found this means that the process took too long. If you delete the formula, wait a second then drag the formula down from the cell above it will find it ok.
If #Ref is shown, this means that no results were returned. This was generally the case where the film name contained (Unrated) or (Extended Edition) etc. If you alter the name it usually finds it, the only movie I couldnt find was Holiday Inn for some reason.
Other words of warning, remove special characters like "?" from file names as this causes the echo script to fail. I think the US store URL is returned as default, you may need to update the Query URL formula to include the Store attribute if you have movies elsewhere (see Apples documentation)
Hope it helps some of you.
Link to Google Sheet
https://docs.google.com/spreadsheets/d/1Kcj3T05FWlMnnoRAXGMu5s4BeyXgjyaXDQqVJkJZ-nc/edit?usp=sharing